Conventional in-line roller skates include an upper boot secured to or integrally formed with a rigid or semi-rigid base. The base in turn is secured along its length, including at heel and toe ends, to a rigid frame. A plurality of wheels are journalled along a common longitudinal axis between the sidewalls of the frame. During use the skater alternatingly strokes on the left and right skates, thrusting off of one skate while gliding on the opposing skate. The ability to fully complete a thrust and thereby achieve maximum forward momentum is limited, however, because of the rigid frame being secured to the heel and toe of the skater's foot.
Because of the rigid, inflexible securement of the frame and base of such skates, a skater attempting to achieve optimal speed during skating may adopt a skating stroke that does not entail plantarflexing of his or her ankle during the push-off phase of the stroke. The term "plantarflex" refers to the rotation of the foot relative to the leg within a plane defined by the leg, where the forefoot moves distally relative to the leg. By avoiding plantarflexion at the ankle, all skate wheels remain on the ground, with the skate base and frame parallel to the ground. The skate thus does not pivot significantly on the forwardmost wheel. Alternately, a skater may adopt a stroke style entailing plantarflexion of his or her ankle during the skate stroke, allowing the forefoot to move distally of the leg, thereby allowing the calf muscles to generate more power during the skate stroke. Due to the rigid nature of the frame and base however, this causes the skater's ankle to elevate excessively off the ground, and may be uncomfortable for the skater. This also entails excessive movement of the skater's upper body and legs, and entails excess wear of the front wheel.
In-line skates with wheels supported on first and second separate frame sections, secured beneath the toe and heel of the skate, such that the foot can flex during the skating stroke, have been proposed. For example, U.S. Pat. No. 5,634,648 discloses a skate including a boot having a rigid toe portion pivotally coupled at the lateral sides of the foot to a rigid heel portion. A first frame segment supporting two wheels is secured beneath the toe section, and a second frame segment supporting two additional wheels is secured beneath the heel section. A tab extends rearwardly from the base of the toe section and is received within a corresponding slot formed in the base of the heel section. During use the skater is able to flex the foot at the sidewall pivot point of the upper, with the tab flexing along its length, so that the heel and rear frame section can elevate off of the ground. While permitting flexion of the foot, flexion is not centralized or primarily occurring at the metatarsal head of the skater's foot, as is anatomically preferred. Thus flexing may be uncomfortable. Additionally, because the boot flexes rearwardly of the front frame and wheels, an unstable platform is provided by the forward segment of the frame during thrusting with the heel elevated. Further, because the two frame segments are separated and uncoupled at all times, there is no lateral rigidity of the frame, even when both frame sections are on the ground. Thus, except to the limited extent provided by the pivot joints between the heel and toe sections of the upper and the forward to rearward tab, there is no torsional rigidity of the skate, as would be desired for straight tracking of the skate.
An alternate flexing skate has been proposed in European patent application EP 0 778 058 A2. A skate is disclosed having an upper boot with a separate toe segment that is slidably received within the forward end of a rear boot segment, and which is pivotally joined to the rear boot segment immediately below the base of the skate. Forward and rearward frame sections are secured beneath the forward and rearward segments of the boot. The rear ends of the sidewalls of the forward frame section overlap the forward ends of the sidewalls of the rear frame section. A second pivot pin is secured through aligned apertures in the forward frame section sidewalls and through corresponding slots in the overlapped sidewalls of the rear frame section. During use the boot pivots to allow the foot to flex during thrusting, with the slotted rearward frame section moving on the second pivot pin retained by the forward frame section. Thus, a limited degree of flexure is provided, with the pivotal coupling of the frame segments also providing a degree of lateral stability and torsional stiffness.
The degree of flexion of such a skate disclosed in the European '058 application is limited, however, by the relatively short length of the slots formed in the rearward frame section. Further, the upper or lower positioning of the rear end of the skate is controlled solely by force applied by the user's foot and leg. During the portion of the skating stroke where the user would desire the wheels to be commonly aligned on the ground in a flat line, the rear of the skate may thus undesirably bump upwardly and downwardly. An alternate embodiment of a skate disclosed in the same European '058 application has a rigid full-length frame and an unsecured rear boot portion which can be lifted off of the frame for flexure during the stroke. However, there is no provision for laterally stabilizing the heel of the boot relative to the frame, such that undesired torsional or lateral movement of the boot relative to the frame may be encountered. Additionally, as in the segmented frame embodiment, the heel may lift undesirably from the frame at inappropriate times.